From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758187AbbBEQkp (ORCPT ); Thu, 5 Feb 2015 11:40:45 -0500 Received: from terminus.zytor.com ([198.137.202.10]:52537 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753099AbbBEQkm (ORCPT ); Thu, 5 Feb 2015 11:40:42 -0500 Message-ID: <54D39CB7.6080504@zytor.com> Date: Thu, 05 Feb 2015 08:39:19 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Ingo Molnar CC: Peter Zijlstra , Linus Torvalds , jsrhbz@kanargh.force9.co.uk, christoph.muellner@theobroma-systems.com, linux@roeck-us.net, linux@rasmusvillemoes.dk, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, akpm@linux-foundation.org, maxime.coquelin@st.com, linux-kernel@vger.kernel.org, martink@posteo.de, tytso@mit.edu, linux-tip-commits@vger.kernel.org Subject: Re: [tip:core/types] bitops: Add sign_extend8(), 16 and 64 functions References: <1421083370-24924-1-git-send-email-martink@posteo.de> <20150119100439.GN25256@twins.programming.kicks-ass.net> <54C00A7B.1000808@zytor.com> <20150205071734.GA3203@gmail.com> In-Reply-To: <20150205071734.GA3203@gmail.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/04/2015 11:17 PM, Ingo Molnar wrote: >>> >>> Even for the 8bit ones? Since we have the *H and *L register >>> we have more 8 bit regs than we have 16/32 bit regs and it >>> might just be worth it. >> >> Fewer, actually. gcc doesn't really use the H registers much, > > Is that true for other compilers as well? > Probably. It wrecks havoc on register allocation, and it doesn't buy that much, especially on 64 bits where all the registers can be used for 8-bit operations. -hpa